The structure and paramutagenicity of the R-marbled haplotype of Zea mays.

Paramutation is the meiotically heritable silencing of a gene that can occur in particular heterozygous combinations. The R-marbled (R-mb) haplotype is paramutagenic: it causes paramutable r1 haplotypes like R-r to become heritably silenced. R-mb was found to comprise three distinct r1 genes arranged as direct repeats. The most distal gene of R-mb, Scm, contains a novel transposable element, Shooter (Sho). Excision of the Sho element early in aleurone development results in the characteristic "marbled" aleurone pigmentation pattern conferred by R-mb. The effect of gene copy number on the paramutagenic strength of R-mb was tested. Paramutagenic strength of R-mb is directly correlated with r1 gene copy number. Paramutagenic strength of R-mb is directly correlated with r1 gene copy number. Paramutagenic strength of R-mb was not affected by removal, through crossing over, of the Sho transposon. Finally, R-mb does not appear to contain the transposable element, Doppia, which is associated with paramutability of R-r, and has been suggested to play a role in paramutagenicity of another paramutagenic haplotype, R-stippled.